This invention relates to substantially nonaqueous persistent thixotropically gelled fire suppressant compositions wherein a carrier material is permeated with a fire suppressant agent and is suspended in a thixotropically gelled fire extinguishing dispersant in which the carrier material is insoluble. When the suppressant composition is dispersed from any suitable container onto an object in the vicinity of the combustion, the fire is extinguished and reignition is prevented by the release of the suppressant agent permeating the carrier material over a period of time.
Several available fire extinguishing compositions are presently capable of extinguishing a fire, however, the problem of reignition still remains a high probability if hot spots and a fuel source remain present. These conditions are present in aircraft engine nacelles, on and off-road vehicles, engine and power train compartments, live electrical wire installations, motors, upholstery, etc.
The compositions of the present invention contain both extinguishing materials to quickly extinguish a fire and means for suppressing further combustion of combustible objects which are potential fuel sources.
Many prior art compositions, particularly in the form of aqueous forms, are claimed to have persistent qualities. Foam extinguishment involves the expansion of water with air or other gases to form a sticky, but flowable, stabilized foam. A layer of foam deposited on a burning object coats and separates the fuel from the flame front, minimizes contact with oxygen and provides some cooling action. Thus, the fire is smothered. Foams are generally inexpensive and relatively easy to apply on a large scale. One of their major advantages is that they will persist for many hours and prevent reignition. However, the quantities of water needed for the foam fire extinguishing agents are too great for portable units and they cannot be used on electrical fires. Also, post-fire clean-up can be a problem.
Another type of extinguishing material includes vaporizing liquid extinguishers. The flame interference of these extinguishers is believed to be due to thermal decomposition of the vaporizing liquid to give low concentrations of flame inhibitors which quench the chemical reactions of the flame. Chlorinated fragments, as from carbon tetrachloride and brominated fragments (as from bromochloromethane) are effective. The rate of thermal decomposition, which should be rapid, volatility, which should be intermediate, and mode of application are significant.
Dry powder extinguishing agents have also found widespread use. While it was initially thought that dry powder extinguishants functioned by decomposition to give CO.sub.2 (which would smother the fire), it has been established that this is not the case. There is little measurable decomposition, and powders which cannot give CO.sub.2 (such as NH.sub.4 H.sub.2 PO.sub.4) are effective. KHCO.sub.3 is twice as effective as NaHCO.sub.3. These materials appear to react by virtue of their chemical surface with the flame propagating intermediates in a flame front. Dry powder clouds are believed also to exert a thermal shielding between the hot flame front and the cooler fuel. The 10-40 micron coated particles generally used appear to be a compromise between the need for a large number of particles (favoring smaller particle size), the need to penetrate the hot gases around the flame and be propelled to the flame front (favoring larger particles), and the need for flowability and storability without packing (hence, the coatings). The dry powders as conventionally used are necessarily very bulky and require relatively large extinguisher tanks.
The following patents disclose various types of fire extinguishing compositions and are believed to represent the closest prior art.
The closest disclosure is believed to be British Patent No. 1,349,508 of Cottrell et al. This patent discloses a fire extinguishing composition in the form of an aqueous gel which produces an incombustible adherent protective layer on burning materials to minimize reignition. The composition comprises an aqueous gel made by at least partially neutralizing an aqueous solution of an alkali metal silicate with an organic or inorganic acid or acidic salt. The acids preferred are those which, besides having a gelling agent themselves, possess some fire-fighting properties, for example phosphoric acids, boric acids and salts thereof. Although the precise chemical structure of the gels is not known, the gels are stable to mechanical agitation. In other words, the gels are not thixotropic.
The ingredients of the patented composition initially may be in the form of powders to be mixed with and dissolved in water to form the aqueous gels. Flow additives such as precipitated silica may be added to the powders to prevent caking on storage or transport or to aid the flow of the powder into a dissolution vessel or water stream. Other compounds may be added to the aqueous mixture before or after gelling. The additives may modify the viscosity of the gel to make it more suitable for spraying or to modify the surface properties of the gel to aid its flow or conversely to increase the adhesion of the gel to the surfaces of combustible material.
The Cottrell et al. patent also discloses incorporating an organic compound, which may be for example a fire-retardant compound, into the gelling composition and allowing the volatilization of the organic compound to blow the composition to a foam. Suitable compounds include fluorocarbons optionally containing chlorine and/or bromine and preferably containing not more than 3 carbon atoms. Especially suitable compounds are disclosed as being bromochlorodifluoromethane, bromopentafluoroethane, dibromodifluoromethane, 1,2-dibromotetrafluoroethane, and bromotrifluoromethane. The addition of 1 to 5 percent of high surface area silica to the composition containing volatile fluorocarbons is disclosed as being advantageous because the undesirable phase separation of components on storage is minimized.
The Cottrell et al. patent neither discloses nor suggests the present invention. The present invention relates to a thixotropically gelled fire extinguishing composition wherein a fire suppressant agent permeates a carrier material. The carrier material permeated with suppressant agent is insoluble in a fire extinguishing dispersant agent into which it is suspended. The entire composition of the present invention is then thixotropically gelled to provide a stable suspension which is easily transported and dispensed. The permeated carrier material adheres to objects in the vicinity of combustion to suppress combustion by slowly releasing the suppressant agent permeating the carrier material.
Moroever, the gelled dispersant agent does not itself adhere to the object. Rather, the dispersant agent almost immediately volatizes to disperse the permeated carrier material and to smother, cool and combine with the free radicals of the combustion process to break the combustion chain, thereby extinguishing a fire to which the composition is applied. Cottrell et al. does not disclose a composition containing insoluble carrier material permeated with fire suppressant agent which is suspended in a thixotropically gelled fire extinguishing dispersant agent.
U.S. Pat. No. 3,402,665 of Tarpley, Jr. et. al. discloses a non-pyrotechnic disseminator wherein the material to be disseminated may comprise finely divided powders suspended within a thixotropically gelled liquid which comprises at least a portion of liquefied gas. The only mention in this patent that the material has use as a fire extinguisher is a statement that all of the gelled liquid may consist of a liquefied gas, giving a composition having primary utility where the liquefied gas has the property of augmenting the functionality of the finely divided powder, as in the case of liquefied Freon being used in a fire extinguisher. There is no disclosure or suggestion in the patent that a fire suppressant agent permeates a carrier material resulting in a persistent fire suppressant composition.
British Patent No. 1,236,075 of Hollows discloses a nonaqueous fire extinguishing liquid, for example, bromochlorodifluoromethane, and a specific finely divided fire extinguishing powder. The powdered fire extinguishing material can be in the form of a dispersion or suspension in the fire extinguishing liquid, these states being assisted if desired by suitable dispersing agents. One or more of the known perhalocarbon liquid propellents can be mixed with the composition or its components. The specific fire extinguishing powder is that disclosed and claimed in British Patent No. 1,168,092 of Birchall which comprises the reaction product between urea and bicarbonates, carbonates, sesquicarbonates and hydroxides of sodium and potassium, having an empirical molecular formula of MC.sub.2 N.sub.2 H.sub.3 O.sub.3, where M represents an atom of potassium or sodium.
German Auslegeschrift No. 1,211,493, dated Feb. 24, 1966, discloses a fire extinguishing composition especially for hand fire extinguishers consisting of a mixture of solid fire extinguishing powders, especially those based on carbonates, phosphates and sulfates, and liquid fluorinated (halo) paraffins, especially bromodifluoromethane and/or bromotrifluoromethane, which simultaneously act a propellants.
Australian Patent No. 227,557 of Warnock et al. discloses a dry chemical fire extinguishing composition comprising a dry chemical fire extinguishing powder, a powdered adsorbing agent and a gaseous expellant, a portion of the gaseous expellant being adsorbed by the adsorbing agent in an amount to maintain internal gaseous pressure in the container at a predetermined pressure at room temperature, the total amount of the gaseous expellant in the container being capable of expelling substantially most of the dry chemical in the container. The adsorbing agent can be silica gel, activated charcoal, attapulgus clay, synthetic zeolites, activated alumina, cracking catalysts of the type used in petroleum refining containing silica and various proportions of alumina, as well as the high surface area porous materials disclosed in U.S. Pat. Nos. 2,866,760. The expellant gas comprises a halogenated hydrocarbon and a gas selected from the group consisting of carbon dioxide, nitrogen, ethane, nitrous oxide and air.
U.S. Pat. No. 3,258,423 of Tuve et al. discloses a fire extinguishing composition known as "light water". It comprises potassium bicarbonate which may be silicone coated, water and particular types of perfluoro surfactants which form a stable foam when aerated with a gas, such as air or difluorodichloromethane. It is disclosed that the foam blocks the feedback of radiant energy to a fuel surface and prevents further release of flammable vapor after the flames have been suppressed, to prevent reignition of burning liquids, particularly.
U.S. Pat. No. 3,267,030 of Dessart discloses a dry powder type of fire extinguishing composition comprising 80-98% of a finely divided alkali metal bicarbonate, 1-19% of talc and 1-8% of very fine grain silica. The alkali metal bicarbonates may be coated with silicone oil. The composition is disclosed as possessing excellent compatability with foams and excellent mobility.
U.S. Pat. No. 3,609,074 of Rainaldi et al. discloses a flame extinguishing foam forming composition containing 5-25 weight percent of a bromine containing halogen saturated alkane of low carbon number (C.sub.1 to C.sub.6). The composition also contains substances conventional in foaming liquid flame extinguishing compositions, such as water, emulsifiers or foam stabilizing surfactants, propellents, antifreezing liquids, corrosion inhibitors, buffer substances, and thickening and carrying agents. Sodium silicates or potassium silicates are disclosed as the thickening and carrying agents.
U.S. Pat. No. 3,655,554 of Fink et al. discloses fire extinguishing compositions, such as foam forming liquids containing surface active substances, which are enhanced by incorporating into the agent about 1-10 weight percent of finely dispersed silica. It is preferred that the silica be present in the fire extinguishing liquids in colloidally dissolved form. The foaming agent and/or foam stabilizer may be mixed with the finely dispersed silica in dry form to obtain a powder which is then added to water to form the foam.
U.S. Pat. No. 4,042,521 of Dunn discloses a dry fire extinguishing composition comprising between about 50-95% of an alkali metal bicarbonate or alkaline earth metal carbonate and between about 50-5% of a metal silicate. Very small amounts of desiccants, such as magnesium stearate, talc, silica, silica gel, diatomaceous earth, calcium chloride, etc., may be added to the dry fire extinguishing composition to prevent the tendency of the composition to cake or agglomerate when subjected to moisture over long periods of time. The composition is disclosed as being effective in preventing flashback or reignition, particularly of Class B fires.
The composition of the present invention is neither disclosed nor suggested by any of the above-identified references and represents an improvement in persistent fire extinguishing and suppressing compositions.